The subject application relates generally to headers for agricultural harvesters. In particular, the subject application relates to an improved automatic header height control system.
Agricultural harvesters such as combine harvesters are well known apparatuses for harvesting grain crops. An agricultural harvester is typically a self-propelled vehicle which includes a feederhouse and mechanisms downstream of the feederhouse for separating grain from other crop material. A header is attached to the front of the harvester and includes mechanisms for cutting crop, gathering crop and delivering crop to the harvester's feederhouse. A typical crop cutter includes knives which shears crop near the ground. After cutting, the crop is gathered e.g., by a harvesting reel which feeds the cut crop to a conveyor system that transports the cut crop to the harvester's feederhouse.
As an agricultural harvester passes over the ground surface, it oftentimes encounters substantial changes in topography. Such changes in land topography can damage the crop cutter which is positioned close to the ground surface.
To address these issues with changing land topography, conventional headers employ height control systems which often include an elaborate array of skid plates, feeler arms, support arms and mechanical sensing mechanisms that must work in concert in order to provide reliable header height adjustment. For example, a typical header includes a chassis and skid plates which extend the entire length of the chassis. Several feeler arms and support arms are spaced along the chassis in the direction of travel of the harvester. As the harvester traverses the ground, the support arms may encounter changes in the underlying ground topography. As the support arms come across such relatively higher and lower spots, they alternately raise and lower the feeler arms. Thus, when a support arm comes into contact with a raised ground portion, such as a mound or the like it pushes up against and raises its associated feeler arm, and when it encounters a depression in the ground it lowers the feeler arm. In conventional mechanical header height adjustment systems, sufficient displacement of any of the feeler arms either upwardly or downwardly produces a corresponding motion in a respective left or right electromechanical sensor mechanism which, in turn, causes hydraulic header adjustment cylinders in communication with the sensor mechanisms to raise, lower or tilt the header chassis whereby it can accommodate the change in ground contour.
In addition to the overall complexity of conventional mechanical header height control systems, the electromechanical sensor mechanisms of such systems are typically constructed as a complicated array of levers, tie rods, springs and sensors which must be continually recalibrated for optimum header height adjustment performance. Such repeated adjustment can be time consuming, especially in regions where the fields being harvested possess many prominent topographical irregularities. Moreover, manual adjustment of the many movable sensor components does not always translate into reliable sensor performance. That is, the precision of the electromechanical sensor mechanism depends in large part on the skill and experience of the individual making the adjustments to the several components of the mechanism, which can vary considerably from person to person.
Still further, the feeler rods of conventional automatic header height control systems are typically disposed more than a foot, even up to 18+ inches, behind the crop cutter. A disadvantage of such spacing is that there is a delay from the time the skid plates encounter a dip or rise in the ground surface and such irregularity is detected by the feeler rod. As a consequence, the crop cutter may suffer damage as a result of its blades impacting and/or becoming immersed in soil if there is a sudden rise in the ground surface. Conversely, if there is a substantial drop in the ground surface level, the cutter may sever less crop than it otherwise should in order to maximize crop yield.